The rapid development of the wired broadband access technology and the requirements of low costs make the optical fiber gradually replace the currently as copper wire (wired) system, i.e., optical in copper out to be a trend. Since the passive optical network (PON) has the properties of being widest, most rapid, and most environment friendly, and the long reach passive optical network can flatten and simplify the network structure and adapt to those network structures with relatively long distance and the investment costs thereof are reduced, most operators accept it and start to or prepare to deploy it so as to meet the increasing communication users and more rapid and better service demands.
Long reach passive optical network is a point-to-multipoint fiber access technology, and as shown in FIG. 1, it includes an optical line termination (OLT), an optical network unit (ONU), an optical distribution network (ODN), etc. Usually, long reach passive optical network is a point-to-multipoint structure composed of one OLT connecting to a plurality of ONUs by way of an optical power separator (abbreviated as optical splitter) and a reach extender box (REB) at the ODN.
Regarding the investment costs and the multiplexing feature of the ODN, a plurality of PON systems may share the same ODN in the passive optical network. As shown in FIG. 2, different PON systems usually have different uplink/downlink wavelengths, for example, the downlink wavelength of GPON is 1480 nm-1500 nm, and the uplink wavelength thereof is 1290 nm-1330 nm, while the downlink wavelength of XG-PON1 is 1575 nm-1580 nm, and the uplink wavelength, thereof is 1260 nm-1280 nm. Therefore, as to such coexisting PON systems, one WDM1r coupler is needed so as to enable two PON systems to coexist on the same ODN, as details are shown in FIG. 2. The design of reach extender box needs to take this demand into consideration. Those past reach extender boxes are mainly designed for a single PON system, and as to the ODN on which a plurality of PON systems coexist, the original reach extender box designed for the single PON system cannot meet the requirements of the actual application, and a combined reach extender box is needed.